20 INTRODUCTION 
the corolla. In a large proportion of the wild 
flowers the petals seem to be more or less united 
to form the corolla, which commonly has lobes, 
each lobe representing a single petal. 
In the case of many flowers one set of these 
floral envelopes, as the calyx and corolla are 
sometimes called, is absent. The botanists gener- 
ally assume that it is the corolla which is absent 
and call the part present the calyx. If these so- 
called sepals look like petals they are said to be 
petaloid sepals. 
In the case of the Lilies and many related 
flowers there are three outer sepals and three 
inner petals which are very similar to one another. 
The six together are said to form the perianth 
and any one of them is called a perianth segment. 
This seems a rather technical term and it is per- 
haps allowable to call these perianth segments 
petals. 
Within the circle of the petals in the Buttercup 
flower there are large numbers of stamens. Each 
stamen consists of a thread-like filament with a 
more or less bag-like anther on its end in which 
is held the powdery pollen. 
Within the circle of the stamens there are sev- 
eral small pisttls. The structure of a typical pistil 
may be well seen in that of a Lily, in which the 
parts are much more distinct than in the case 
of the Buttercup. As may be seen in the Lily, a 
